Syringes are a well-known means of injecting fluids into or removing fluids from living subjects such as humans and animals. Recently, great concern has arisen over the use of these devices due to the potential contamination or infection of medical personnel treating patients with communicable diseases through the accidental puncture of the skin of treating personnel and the resulting transfer of contaminated or infectious fluids.
A variety of systems and devices have been developed for protecting against the potential hazards to medical personnel posed by unprotected syringes. For example, in U.S. Pat. No. 4,477,998 an apparatus is disclosed wherein a spring-loaded mechanism is deployed which advances a protective sheath towards the tip of a hypodermic needle. As the needle is withdrawn, the protective sheath advances beyond the tip of the needle where a movable ball-bearing slides over the tip of the needle to provide a positive locking mechanism which irreversibly encapsulates the tip of the needle. In a system disclosed in U.S. Pat. No. 4,894,055, a needle guard assembly is disclosed wherein a plurality of telescoping concentric members comprising a needle guard are moved into a locking position by a spring biasing member such that movable tabs on an inner member engage a cooperating detent on the inner surface of an outer member to lock the inner member in an extended position. U.S. Pat. No. 4,911,693 also discloses a needle guard assembly having a plurality of telescoping concentric members wherein a first member is fixedly mounted to a syringe body. A second member is movably mounted within the first member and is movable between a first position wherein the needle is unexposed and a second position wherein the needle is exposed. Means are provided for urging the second member towards the first position and means are also provided for permanently locking the second member in a position wherein the needle tip is unexposed. However, in this system, the needle guard is not locked automatically. Specifically, the needle guard portion of the syringe incorporates a tab which engages a "T" shaped groove in the first member. To utilize the syringe, the needle guard is manually rotated 90 degrees to move the tab to a longitudinal groove which allows the tab and needle guard to move to a retracted position for injections. When the injection is complete, the needle guard must be again rotated 90 degrees so the tab engages a transverse portion of the groove to lock the needle guard in the extended position. Numerous other types of needle guard devices are known in the art such as the devices disclosed in U.S. Pat. Nos. 4,935,016, 4,938,745, 4,850,996, 4,664,654, and 4,804,371. All of the above-referenced patents are incorporated herein by reference.
While each of the above-mentioned patents describe needle guard devices which may function satisfactorily, no device is known which provides automatic, positive and fail-safe performance while simultaneously providing a device which is easily manufactured, utilizes a minimum of moving parts, which provides minimal interference when the syringe is used on a patient, and which is highly distinctive and recognizable as containing a potentially hazardous substance.